The present invention relates to a shutter mechanism of a camera casing installed on a vehicle, and more particularly relates to a shutter mechanism capable of releasing a shutter from the casing when the shutter freezes to the camera casing.
An automotive camera is installed on a vehicle body for outdoor use. Such outdoor cameras are usually subjected to severe weather conditions including rain and snow. To protect the camera, the camera casing is usually equipped with a shutter. The shutter is closed when the camera is not used for photographing. The outside air temperature decreases in the winter season. The water or moisture component entering in a narrow space between the casing and shutter may freeze in such a low temperature condition. When the shutter freezes to the casing, a very large force is required to release the shutter from the casing against the binding force of ice. For this reason, the shutter is driven by a high-power motor. Alternatively, it is possible to provide another mechanism which is specially operable for releasing the frozen shutter from the camera casing. In this case, the shutter may be opened or closed by using a low power motor.
FIGS. 6A and 6B cooperatively illustrate a shutter motion of a conventional camera casing. As shown in FIG. 6A, a shutter 103 of length L is swingable about a hinge 104 provided at an edge of the shutter 103. FIG. 6B shows a closed condition of the shutter 103. In this closed condition, the water or moisture component may freeze in a narrow space between shutter 103 and the casing 102. To release the shutter 103 from ice 110 by a pulling force F, a torque of approximately Fxc3x97L/2 is required.
FIGS. 7A and 7B cooperatively illustrate a shutter motion of another conventional camera casing. As shown in FIG. 7A, a shutter 203 is similar to a quarter pipe and is swingable about a rotary shaft 204. FIG. 7B shows a closed condition of the shutter 203. When water or moisture component freezes in a narrow space between the shutter 203 and the casing 202, the shutter 203 needs to be released from the ice 210 by using a shearing force. It means that a very large torque is required to release the shutter 203 from the ice 210.
The above-described conventional shutter mechanism requires a large torque to release the shutter from the camera casing when the shutter freezes to the camera casing. It may be possible to employ a special releasing mechanism. However, the structure of the shutter mechanism will be complicated and the cost is increased. A low-power motor may be used for producing a large torque. However, it requires an enlarged size speed-reducing gear mechanism. When the speed-reducing gear mechanism has a large gear ratio, the open/close motion of the shutter becomes slow. It takes a relatively long time to open or close the shutter.
An object of the present invention is to provide a shutter mechanism which is capable of releasing the shutter from the camera casing by using a low-power motor when they freeze together and also capable of promptly accomplishing the open/close operation of the shutter.
In order to accomplish this and other related objects, the present invention provides a shutter mechanism comprising a rotary plate having an eccentric shaft and an engaging portion which are spaced from a rotary shaft. A driving member, such as a motor, is provided to drive the rotary plate. A swing arm of a shutter is connected to the eccentric shaft and rotatable about the eccentric shaft. An engaging member is provided on the swing arm. The swing arm is integrated with the rotary plate when the engaging portion of the rotary plate engages with the engaging member. And, the engaging member is disengaged from the engaging portion when a large torque acts on the swing arm.
With this arrangement, it becomes possible to release the shutter from the camera casing by using a low-power motor even when the shutter freezes to the camera casing. And also, it becomes possible to promptly accomplish the open/close operation of the shutter.
More specifically, the present invention provides a shutter mechanism comprising a rotary plate having an eccentric shaft and an engaging portion spaced from a rotary shaft of the rotary plate, a driving member for driving the rotary plate about the rotary shaft, a swing arm connecting a shutter to the eccentric shaft and rotatable about the eccentric shaft, and an engaging member provided on the swing arm, wherein the swing arm is integrated with the rotary plate when the engaging portion of the rotary plate engages with the engaging member of the swing arm, and the engaging member is disengaged from the engaging portion when a predetermined torque acts on the swing arm. The eccentric shaft is located near the rotary shaft. A small torque can be converted into a large force which is available for releasing the shutter from the camera casing even when the shutter freezes to the camera casing.
Preferably, the positional relationship between the eccentric shaft and the engaging portion of the rotary plate is determined in such a manner that the engaging member is separated from the engaging portion when the shutter is located at a predetermined closed position, the shutter moves linearly when the rotary plate starts rotating, the engaging member engages with the engaging portion after the rotary plate rotates a predetermined angle, thereby allowing the shutter to rotate. With this arrangement, it becomes possible to generate a strong force for releasing the shutter from the camera casing even when they freeze together. The shutter can be quickly opened.
Preferably, the engaging portion is provided in an opposed relationship with the eccentric shaft across the rotary shaft.
Another aspect of the present invention provides a method for driving a shutter connected to an end of a swing arm by rotating a rotary plate about a rotary shaft, wherein the swing arm is connected to an eccentric shaft spaced from the rotary shaft. The method comprises the steps of engaging an engaging portion with an engaging member in accordance with a rotation of the rotary plate so as to integrate the swing arm with the rotary plate and rotate the shutter together with the swing arm, and disengaging the engaging member from the engaging portion when a predetermined torque acts on the swing arm to cause the shutter and the swing arm to move linearly via the eccentric shaft. According to this method, a small torque can be converted into a large force which is available for releasing the shutter from the camera casing when they freeze together. The shutter can be airtightly closed by the large force.
Preferably, the engaging member is disengaged from the engaging portion when the shutter is in a predetermined closed condition or in a predetermined opened condition, so that the swing arm moves linearly along the track or trail of the eccentric shaft immediately after the rotary plate starts rotating or immediately before the rotary plate stops rotating. According to this method, a large force is available for opening and closing the shutter and the shutter can rotate speedily during the open/close motion.